The present invention relates to teaching systems and particularly to improvements to wireless teaching systems.
In recent years electrical teaching systems have found considerable application in the teaching environment and particularly in language labs where the student is required to listen to spoken foreign languages to learn the proper pronunciation and in turn practice such pronunciation. Typically this is accomplished by microphones and headsets such that the student can also hear his or her pronunciation and compare it with that of the lesson source. Language labs and other teaching systems frequently must provide the same lesson material for several students while at the same time providing different lesson sources for other students who utilize the facilities.
There exists several systems capable of this basic operation, some of which are directly wired units such as represented by U.S. Pat. No. 3,200,516 issued on Aug. 17, 1965, to D. O. Parker and assigned to the present assignee. Wired systems although adequate for providing the teaching functions, require considerable installation expense and lack the flexibility of wireless systems which permit relatively easy installation are portable and can be moved from classroom to classroom if desired. Several wireless type systems have also been developed in recent years. U.S. Pat. No. 3,122,847 issued Mar. 3, 1965, to R. H. Redfield et al and U.S. Pat. No. 3,623,242 issued Nov. 30, 1971, to E. L. Hoover, are representative of wireless systems. Although these wireless systems represent a significant advantage and improvement over systems which must be directly wired between the instructor's console and the student's units; the prior art wireless systems have required a plurality of operating frequencies to provide intercommunication and monitoring of the student by the instructor. Thus, for example, in the above noted Hoover patent each student has a predetermined assigned frequency unique to the student requiring at the instructor's console, a plurality of oscillators such that the frequency of the instructor's transmitter must be changed each time the instructor wishes to either monitor or intercommunicate with one of the students. Such an arrangement using multiple frequencies, one for each student in the system, by virtue of its relatively complex circuitry with multiple crystal oscillators and matched crystal filters can be costly to manufacture and failure prone.